The present invention relates to an aircraft fuel tank arrangement for the relief of a pressure differential between the interior of the aircraft fuel tank and the ambient atmosphere.
The presence of a significant pressure differential across the inner and outer surfaces of an aircraft fuel tank can be undesirable. If the pressure differential is too high, there is a risk that the fuel tank may implode or explode, leading to a loss of fuel and rupture to the surface of the wing skin of an aircraft. Such ruptures may be uncontrolled and therefore potentially dangerous. Such pressure differentials may be positive (in which case the pressure on the inside of the fuel tank is higher than on the outside of the fuel tank) or negative (in which case the pressure on the outside of the fuel tank is greater than the pressure inside the fuel tank). Such pressure differentials may occur at various times during operation of the aircraft (for example, during fuelling, refuelling, defueling and when the aircraft is making certain manoeuvres). For example, when an aircraft climbs the pressure inside the tank typically exceeds that outside the tank. Conversely, when an aircraft descends the pressure inside the tank is typically lower than the pressure outside the tank.
Relief of excessive pressure differentials has been addressed in several ways. A simple yet effective solution is to provide what is known as a stackpipe (effectively a tube) which extends from the outer surface of the fuel tank (which typically forms an outer surface of the aircraft) into the interior of the fuel tank. A burst disk is provided at the end of the stackpipe which is inside the fuel tank. The interior surface of the burst disk is subjected to the pressure inside the fuel tank and the exterior surface of the burst disk is subjected to the pressure outside the fuel tank (ambient atmospheric pressure). At a predetermined pressure differential (less than the pressure differential required to cause a rupture of the fuel tank) the burst disk will rupture, thereby allowing rapid equalisation of pressure and preventing an undesirable increase in the pressure differential which otherwise may cause the wing fuel tank to rupture. The stackpipe ensures that any fuel below the open end of the stackpipe inside the fuel tank remains inside the fuel tank. It has been discovered, however, that the cavity formed beneath the stackpipe and burst disk may lead to acoustic resonance when the aircraft is in motion, such resonance creating noise (typically a whistle) and occasionally leading to unwanted rupture of the burst disk. This is obviously, undesirable. The resonance problem has been successfully addressed by placing a gauze across the middle portion of the stackpipe.
An alternative solution to the alleviation of pressure differentials is to provide the fuel tank with a valve operable to allow rapid equalisation of pressure. Such valves are reusable and therefore offer certain advantages over the simple burst disk. However, such valves are relatively expensive and typically comprise moving parts, and therefore require regular inspection to ensure that the valve will operate when required to do so.
The object of the present invention is to ameliorate one or more of the problems mentioned above.